Conventional servo motor systems usually employ position detectors to enable the provision of the most effective position commands for driving the motor, and thereby to maximize operating efficiencies. The incorporation of such a device adds substantially to the cost and complexity of the motor system, however, and also increases the difficulty of utilizing it most effectively.
Stepping motor systems inherently afford high positioning performance and other beneficial attributes; because no position detection device is needed, moreover, they of course avoid the attendant disadvantages. On the other hand, practical operation of such motors requires the Application of excessive drive currents so as to ensure that synchronism is maintained. Thus, and despite load changes, the current supplied must be set for the maximum that would normally be employed during acceleration; typically, the current utilized to drive a stepping motor is at least double that which is actually demanded by the load. Substantial amounts of energy are wasted (as excessive heat) as a result, thereby rendering such systems relatively inefficient in respect of power consumption.